1. Field of the Invention
The present invention relates to a drum washing machine, and in particular to a dehydration control method of a drum washing machine which is capable of preventing vibration and noise due to excessive eccentricity and securing reliability of eccentricity sensing.
2. Description of the Prior Art
In general, a drum washing machine performs a dehydrating process through a uniforming process after a cleaning process is finished. Herein, the uniforming process is for uniforming the laundry tangled in the cleaning process, tangle of the laundry is loosened by separating the laundry from the internal wall of a drum by rotating the drum at a low speed. And, after the uniforming process is finished, in the dehydrating process, the drum is rotated at a high speed in the opposite direction of the uniforming process, and accordingly moisture contained in the laundry is removed.
Herein, when the drum is rotated at a high speed in the dehydrating process and the laundry is eccentrically placed in the drum, vibration and noise occur, various parts installed inside the washing machine may be damaged or dehydration performance may be lowered.
Therefore, the drum washing machine senses eccentricity of the laundry stored in the drum after the uniforming process and determines whether it proceeds the dehydrating process.
FIG. 1 is a flow chart illustrating a dehydration control method of a drum washing machine in accordance with the conventional art.
As depicted in FIG. 1, in the conventional dehydration control method of the drum washing machine, after the cleaning process is finished, the uniforming process for uniforming tangle of the laundry is performed as shown at step S1, when the uniforming process is finished, the drum is rotated in the opposite direction of the uniforming process up to a set speed as shown at step S2. And, when a rotational speed of the drum reaches the set speed, RPM variation of a driving motor rotating the drum is measured as shown at step S3.
Eccentricity of the laundry is measured on the basis of the RPM variation of the driving motor, the measured eccentricity is compared with a preset reference eccentricity, when the measured eccentricity is within the range of a permitted limit, the dehydrating process is performed, when the measured eccentricity exceeds the permitted limit, the uniforming process is re-performed as shown at steps S4 and S5.
As described above, when the measured eccentricity is greater than the reference eccentricity, the uniforming process is re-performed in order to lower the eccentricity of the laundry so as to be within the permitted limit.
However, in the conventional dehydration control method of the drum washing machine, because eccentricity of the laundry is judged by measuring RPM variation of the driving motor only in one case, a measuring result is not accurate. Particularly, because diagonal eccentricity can not be sensed accurately, reliability of an eccentricity measuring value is lowered.
Herein, the laundry may be arranged eccentrically in many ways, however, it can be largely divided into forward eccentricity and diagonal eccentricity. In more detail, as depicted in FIG. 2, in taking a side view of a drum 10, when the laundry is placed on only one of a first position 20 and a second position 30, it is called the forward eccentricity, when the laundry is placed on both the first and second positions 20, 30, it is called as the diagonal eccentricity.
When the diagonal eccentricity occurs, in taking a front view of the drum 10, it looks as if eccentricity does not occur, however, RPM variation is different from that of the forward eccentricity in proceeding of the dehydrating process.
FIG. 3 is a graph showing RPM variation in the forward eccentricity according to an acceleration time increase of the drum in accordance with the conventional art, and FIG. 4 is a graph showing RPM variation in the diagonal eccentricity according to an acceleration time increase of the drum in accordance with the conventional art.
As depicted in FIG. 3, in the forward eccentricity, when the drum is rotated at a low speed, namely, in the early dehydrating process, RPM variation is the greatest, and RPM variation is gradually lowered according to a rotational speed increase of the drum.
As described-above, in the forward eccentricity, because RPM variation is great in the early dehydrating process, it is possible to grasp eccentricity occurrence by measuring RPM variation at an early rotational speed (P) of the drum.
However, as depicted in FIG. 4, in the diagonal eccentricity, early RPM variation is small, then, RPM variation increases according to a gradual rotational speed increase of the drum. Because RPM variation is measured at one fixed rotational speed (P) in the early dehydrating process in the conventional art, it is impossible to detect eccentricity occurrence, and accordingly reliability of eccentricity sensing is lowered. In addition, because vibration and noise occur due to the eccentricity occurrence, internal parts of the washing machine may be damaged, and a dehydration performance of the washing machine may be lowered.